Institut für Chemie

Permanent URI for this collectionhttps://hohpublica.uni-hohenheim.de/handle/123456789/4

Browse

Now showing 1 - 3 of 3

Exo‐endo Isomerism of carboranes: Unusual geometries of C2B5X7 (X=Cl, Br) and C2B7Cl9 with exo‐skeletal BCl2 groups on carbon revealed by joint spectroscopic/computational studies
(2023) Keller, Willi; Conrad, Jürgen; Hofmann, Matthias
Reexamination of the co‐pyrolysis reactions of B2Cl4 with C2Cl4 at 350 °C and of B2Br4 with CBr4 at 300 °C in vacuo confirmed the carboranes C2B5Cl7 (1), C2B7Cl9 (2), and C2B5Br7 (3) as low‐yield products. While 1 only could be concentrated by repeated vacuum fractionation, 2 and 3 could now be isolated from the conglomerate mixtures for a full spectroscopic characterization and the compounds were verified in their geometries by detailed DFT computations. Surprisingly, the perhalogenated carboranes do not adopt the expected “all‐endo”‐geometries with cluster sizes derived by the sum of the n boron and two carbon atoms (n+2) as known from the syntheses of the parent closo‐carboranes C2BnHn+2. Instead, DFT/GIAO(ZORA)/NMR (GIAO for X=Cl, ZORA for X=Br) computations revealed that the perhalogenated carboranes favor structures with BX2 groups as exo‐skeletal ligands attached to both cage‐carbon atoms yielding the five‐vertex closo‐1,5‐(CBX2)2B3X3 (1: X=Cl; 3: X=Br) and the seven‐vertex closo‐2,4‐(CBCl2)2B5Cl5 for 2. In contrast to these perhalogenated carboranes, analogous computations on the hydrogen substituted carboranes C2BnHn+2, silaboranes Si2BnHn+2 and Si2BnXn+2 (n=5, 7) show in all cases a thermodynamic favorization of structures where all boron atoms of the formula are endo‐skeletally incorporated into the cluster frameworks.
Glucoselipid biosurfactant biosynthesis operon of Rouxiella badensis DSM 100043T: screening, identification, and heterologous expression in Escherichia coli
(2025) Harahap, Andre Fahriz Perdana; Treinen, Chantal; Van Zyl, Leonardo Joaquim; Williams, Wesley Trevor; Conrad, Jürgen; Pfannstiel, Jens; Klaiber, Iris; Grether, Jakob; Hiller, Eric; Vahidinasab, Maliheh; Perino, Elvio Henrique Benatto; Lilge, Lars; Burger, Anita; Trindade, Marla; Hausmann, Rudolf; Seo, Myung-Ji
Rouxiella badensis DSM 100043T had been previously proven to produce a novel glucoselipid biosurfactant which has a very low critical micelle concentration (CMC) as well as very good stability against a wide range of pH, temperature, and salinity. In this study, we performed a function-based library screening from a R. badensis DSM 100043T genome library to identify responsible genes for biosynthesis of this glucoselipid. The identified open reading frames (ORFs) were cloned into several constructs in Escherichia coli for gene permutation analysis and the individual products were analyzed using high-performance thin-layer chromatography (HPTLC). Products of interest from positive expression strains were purified and analyzed by liquid chromatography/electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and nuclear magnetic resonance (NMR) for further structure elucidation. Function-based screening of 5400 clones led to the identification of an operon containing three ORFs encoding acetyltransferase GlcA (ORF1), acyltransferase GlcB (ORF2), and phosphatase/HAD GlcC (ORF3). E. coli pCAT2, with all three ORFs, resulted in the production of identical R. badensis DSM 100043T glucosedilipid with Glu-C10:0-C12:1 as the main congener. ORF2-deletion strain E. coli pAFP1 primarily produced glucosemonolipids, with Glu-C10:0,3OH and Glu-C12:0 as the major congeners, predominantly esterified at the C-2 position of the glucose moiety. Furthermore, fed-batch bioreactor cultivation of E. coli pCAT2 using glucose as the carbon source yielded a maximum glucosedilipid titer of 2.34 g/L after 25 h of fermentation, which is 55-fold higher than that produced by batch cultivation of R. badensis DSM 100043T in the previous study.
Structure elucidation and characterization of novel glycolipid biosurfactant produced by Rouxiella badensis DSM 100043T
(2025) Harahap, Andre Fahriz Perdana; Conrad, Jürgen; Wolf, Mario; Pfannstiel, Jens; Klaiber, Iris; Grether, Jakob; Hiller, Eric; Vahidinasab, Maliheh; Salminen, Hanna; Treinen, Chantal; Perino, Elvio Henrique Benatto; Hausmann, Rudolf; Serianni, Anthony S.
Microbial biosurfactants have become increasingly attractive as promising ingredients for environmentally friendly products. The reasons for this are their generally good performance and biodegradability, low toxicity, production from renewable raw materials, and benefits for the environment perceived by consumers. In this study, we investigated the chemical structure and properties of a novel glycolipid from a new biosurfactant-producing strain, Rouxiella badensis DSM 100043 T . Bioreactor cultivation was performed at 30 °C and pH 7.0 for 28 h using 15 g/L glycerol as a carbon source. The glycolipid was successfully purified from the ethyl acetate extract of the supernatant using medium pressure liquid chromatography (MPLC). The structure of the glycolipid was determined by one- and two-dimensional ( 1 H and 13 C) nuclear magnetic resonance (NMR) and confirmed by liquid chromatography electrospray ionization mass spectrometry (LC-ESI/MS). NMR analysis revealed the hydrophilic moiety as a glucose molecule and the hydrophobic moieties as 3-hydroxy-5-dodecenoic acid and 3-hydroxydecanoic acid, which are linked with the glucose by ester bonds at the C2 and C3 positions. Surface tension measurement with tensiometry indicated that the glucose–lipid could reduce the surface tension of water from 72.05 mN/m to 24.59 mN/m at 25 °C with a very low critical micelle concentration (CMC) of 5.69 mg/L. Moreover, the glucose–lipid demonstrated very good stability in maintaining emulsification activity at pH 2–8, a temperature of up to 100 °C, and a NaCl concentration of up to 15%. These results show that R. badensis DSM 100043 T produced a novel glycolipid biosurfactant with excellent surface-active properties, making it promising for further research or industrial applications.

Browse

Browsing Institut für Chemie by Person "Conrad, Jürgen"